High index and high impact resistant polythiourethane/urea material, method of manufacturing same and its use in the optical field

ABSTRACT

A transparent, non elastomeric, high index, impact resistant polythiourethane/urea material comprising the reaction product of:  
     a) at least one (α, ω)-diiso(thio)cyanate cycloaliphatic or aromatic prepolymer having a number average molecular weight ranging from 100 to 3000 gmol −1 , and  
     b) at least one primary diamine, in an equivalent molar ratio amine function/iso(thio)cyanate function from 0.5 to 2, preferably from 0.90 to 1.10, wherein, said prepolymer and diamine are free from disulfide (—S—S—) linkage and at least one of the prepolymer or the diamine contains one or more S atoms in its chain.

BACKGROUND OF THE INVENTION

[0001] 1) Field of the Invention

[0002] The present invention relates to a rigid, optically transparent,high index, impact resistant polythiourethane/urea material, which isparticularly suited for making optical articles such as sun lenses,ophthalmic lenses and protective lenses.

[0003] 2) Background of the Invention

[0004] Plastic materials are widely used in the optical field andparticularly in the ophthalmic field for their lightness, high impactresistance and tintable capability by immersion in a bath containing anorganic dye.

[0005] Optically transparent plastic materials having a high refractiveindex, higher than 1.53, are of major interest since they render itpossible to manufacture optical articles such as lenses of lowerthickness for an equivalent corrective power (optical power).

[0006] Of course, this increase in refractive index of the materialshall not be at the expense of the other valuable properties such astransparency and impact resistance of the material.

[0007] Preferably, other required properties for the lens material are

[0008] non yellowness;

[0009] ability to be treated (by hard coats, primers, . . . );

[0010] density as low as possible—ageing resistance (especiallyphotodegradation resistance).

[0011] U.S. Pat. No. 6,127,505 discloses a transparent, non-elastomeric,high index, high impact resistant polyurethane material which is areaction product of:

[0012] a polyurethane prepolymer prepared by reaction of an aliphatic orcycloaliphatic diisocyanate with at least one OH containing intermediatehaving a rate average molecular weight of from about 400 to 2.000selected from the group consisting of polyester glycols,polycaprolactone glycols, polyether glycols, polycarbonate glycols andmixtures thereof, in an equivalent ratio of about 2.5 to 4.0 NCO/1.0 OHand

[0013] at least one first aromatic diamine curing agent selected fromthe group consisting of 2,4-diamino-3,5, diethyl-toluene,2,6-diamino-3,5,diethyl-toluene and mixtures thereof in an equivalentratio of about 0.85 to 1.02 NH₂/1.0 NCO.

[0014] Unfortunately, the polyurethanes obtained have relatively lowrefractive index, n_(D)²⁵,

[0015] of at most 1.53.

SUMMARY OF THE INVENTION

[0016] Thus, the aim of the present invention is i.a. to provide anoptically transparent, rigid, high index, impact resistant material thatwould particularly be useful for making optical articles.

[0017] By high refractive index material, there is intended in thepresent invention a material having a refractive index, n_(D)²⁵

[0018] higher than 1.53, preferably of at least 1.55 and most preferablyof at least 1.57.

[0019] The above objective is reached according to the invention byproviding a transparent, non elastomeric, high refractive index, impactresistant polythiourethane/urea material comprising the reaction productof:

[0020] a) at least one (α, ω)-di-NCX prepolymer in which X represent Oor S and having a number average molecular weight ranging from 100 to3000 g mol⁻¹, said prepolymer being free from disulfide (—S—S—) linkageand

[0021] b) at least one aromatic primary diamine in a molar equivalentratio NH₂/NCX ranging from 0.5 to 2, preferably 0.90 to 1.10, morepreferably from 0.93 to 0.95, said aromatic primary diamine being freefrom disulfide (—S—S—) linkage, and

[0022] c) at least one of the prepolymer or the diamine containing oneor more sulfur atoms.

[0023] The invention further concerns optical articles such as sunlenses, ophthalmic lenses and protective lenses made of thepolythiourethane/urea material defined above.

[0024] The (α,ω))-diiso(thio)cyanate prepolymer is preferably an(α,ω)-diiso(thio)cyanate cycloaliphatic or aromatic prepolymer and mostpreferably such a prepolymer containing one or more sulfur atoms in itschain.

[0025] These prepolymers can be prepared by reacting an (α, ω)-diol ordithiol prepolymer, preferably further containing at least one sulfuratom in its chain, with one or more cycloaliphatic or aromaticdiisocyanate or diisothiocyanate according to the following scheme:

[0026] (α, ω)-di-XH prepolymer (I)+cycloaliphatic or aromatic di-NCX(II)→(α, ω)-di-NCX prepolymer (III)

[0027] with X=O or S.

[0028] The preferred prepolymers (I) are (α,ω)-dithiol prepolymers,further containing at least one sulfur atom in their chains.

[0029] Among these prepolymers there could be cited the followingprepolymers:

[0030] Prepolymers of formula:

[0031]  where x and y are such that {overscore (M)}_(n) of the resultingprepolymer (III) ranges from 100 to 3000 g mol⁻¹ (these prepolymers canbe made by polymerizing sulfide monomers, such as ethylene sulfide and2-mercaptoethyl sulfide (DMES));

[0032] Prepolymers resulting from the polymerization of diepisulfides offormula:

[0033] in which R¹ and R² are, independently from each other, H, alkyl,aryl, alkoxy, alkylthio or arylthio; R³ and R⁴ are, independently fromeach other,

[0034] R_(a) designates H, alkyl, aryl, alkoxy, aryloxy, alkylthio orarylthio and, n is an integer from 0 to 4 and m is an integer from 1 to6, and

[0035] Prepolymers of formula:

[0036] where n is such that the number average molecular weight({overscore (M)}_(n)) of the prepolymer ranges from 500 to 1500,preferably from 650 to 1350 g mol⁻¹.

[0037] where n is such that the number average molecular weight({overscore (M)}_(n)) of the prepolymer ranges from 500 to 1500,preferably from 650 to 1350 g mol⁻¹.

[0038] A preferred class of diepisulfides is comprised of diepisulfidesof formula:

[0039] in which R¹, R², R³ and R⁴ are defined as above.

[0040] In R¹, R², R³ and R⁴ the alkyl and alkoxy groups are preferablyC₁-C₆, more preferably C₁-C₄ alkyl and alkoxy groups such as methyl,ethyl, propyl, butyl, methoxy, ethoxy, propoxy and butoxy.

[0041] The preferred diepisulfides are those of formula:

[0042] and hyperbranched prepolymers resulting from the polymerizationof the above mentioned diepisulfides, in particular diepisulfides offormulas (I″_(b)) with DMES.

[0043] The prepolymers of formula (I_(c)) constitute a new class ofpolysulfides. These new soft polysulfides have high refractive indexesand can be prepared by thermal and/or photopolymerization, in thepresence of an initiator, of 2-mercaptoethylsulfide (DMES) correspondingformula HS—CH₂CH₂—S—CH₂CH₂—SH and allylsulfide (AS) correspondingformula CH₂═CHCH₂—S—CH₂—CH═CH₂.

[0044] Preferably, prepolymers of formula (Ic) are prepared byphotopolymerization in the presence of a photoinitiator.

[0045] The refractive index of these prepolymers (I_(c)) typicallyranges from 1.57 to 1.62, preferably from 1.59 to 1.615.

[0046] Photopolymerization of prepolymers of formula (Id) is effected bymixing DMES and AS in the required proportions, such that the molarratio Allyl is less than 2, preferably less than 1 and more preferablyless than 0.8, adding at least one photoiniator and irradiating themixture, preferably with an UV light. Preferably, UV light wavelengthwill range from 320 to 390 nm. UV light intensity typically ranges from40 mW to 90 mW and total exposure time to UV light, either in one shotor several shots, ranges from 250 to 1650 seconds, preferably 300 to1500 and more preferably 600 to 1000 seconds.

[0047] Any classical photoinitiator, in usual amount can be used for thephotopolymerization process. Preferred photoinitiators are1-hydroxycyclohexyl phenyl ketone (Irgacure® 184) and2-hydroxy-2-methyl-1-phenylpropan-1-one (Darocur® 1173). The amount ofphotoinitiator used will usually range from 0.05% to 10% by weight,preferably from 1% to 5%, and more preferably from 1 to 2% by weight,based on the total weight of the polymerizable monomers present in thepolymerization mixture.

[0048] Although the photoinitiator may be added to the polymerizationmixture in one shot, generally before starting irradiation, it ispreferred to add the photoinitiator in several shots during irradiationprocess of the mixture. With the addition of the photoinitiator inseveral shots, higher conversion rates of the allylsulfide and higherrefractive indexes are obtained.

[0049] Similarly, thermal polymerisation is effected by simply mixingappropriate amounts of DMES and AS, adding to the mixture an effectiveamount of at least one thermal radical initiator, and heating themixture at a temperature ranging from 30° C. to 80° C., preferably from40° C. to 70° C. Any classical thermal initiator can be used, such asdi(4-tert-butylcyclohexyl) peroxydicarbonate (P16S) and2,2′-azobisisobutyronitrile (AIBN) in usual amounts.

[0050] Typically, the amount of thermal initiator will range from 0.05to 10%, preferably 1 to 8%, by weight of the polymerizable monomerspresent in the mixture.

[0051] The thermal initiator may be added to the mixture in one shot atthe beginning of the polymerisation or in several shots during thecourse of the polymerization process.

[0052] Polymerization is usually effected by bulk polymerization processbut it can also be a solution polymerization process using anyappropriate solvent or mixture of solvents. A preferred solvent istetrahydrofuran (THF).

[0053] The cycloaliphatic or aromatic diiso(thio)cyanate (II) may be acycloaliphatic or aromatic diisocyanate or a cycloaliphatic or aromaticdiisothiocyanate or a mixture thereof.

[0054] Among the preferred cycloaliphatic diiso(thio)cyanate, there maybe cited bis(iso(thio)cyanatemethyl) cyclohexane hexamethylenediiso(thio)cyanate and dicyclohexylmethane diiso(thio)cyanate andmixtures thereof.

[0055] The most preferred cycloaliphatic diisocyanate is Desmodur® W offormula:

[0056] and the corresponding diisothiocyanate of formula:

[0057] Among the aromatic diiso(thio)cyanates, there may be citedtoluene diiso(thio)cyanate, phenylene diiso(thio)cyanate, ethylphenylenediiso(thio)cyanate, isopropylphenylene diiso(thio)cyanate,dimethylphenylene diiso(thio)cyanate, diethylphenylenediiso(thio)cyanate, diisopropylephenylene diiso(thio)cyanate, xylylenediiso(thio)cyanate, 4,4′-diphenylmethane diiso(thio)cyanate, naphtalenediiso(thio)cyanate.

[0058] The preferred aromatic diiso(thio)cyanate is xylylenediisocyanate (XDI).

[0059] The most preferred cycloaliphatic and aromaticdiiso(thio)cyanates are Desmodur® W or the correspondingdiiso(thio)cyanate or mixtures of these compounds with xylylenediisocyanate.

[0060] Usually, the molar ratio NCX/XH of the iso(thio)cyanate group tothe hydroxyl or thiol group, during the reaction, ranges from 1.9 to4.5, preferably from 3 to 3.5.

[0061] The reaction of prepolymer (I) and monomer (II) can be effectedwith or without a polymerization catalyst. Usually, the polymerizationis effected at temperature ranging from 50 to 120° C. When no catalystis used, of course, higher temperatures and longer times ofpolymerization are required.

[0062] Catalyst may be any known catalyst for the polymerization of themonomer.

[0063] Among the useful catalysts, there may be citeddimethyltindichloride, dibutyltindichloride and dibutyltindilaurate,cocatalysts or promoters such as N,N-dimethylcyclohexylamine and1,4-diazabicyclo-[2,2,2]-octane (DABCO) could also be used with thecatalyst to enhance its activity.

[0064] To prepare the final polythiourethane/urea material according tothe invention, the (α,ω)-di-NCX prepolymer (III) is reacted with anaromatic primary diamine according to the following scheme:

(α, ω)-di-NCX prepolymer (III)+aromatic di-NH₂ (IV)→final material

[0065] X=O or S

[0066] During this reaction step, in order to obtain the best propertiesof impact resistance for the material, it is preferred that the molarratio NH₂/NCX be kept in the range of 0.90 to 1.10 and preferably 0.93to 0.95.

[0067] Among the aromatic primary diamines (IV) that may be used in thesecond reaction step, preferred aromatic diamines are those whichinclude at least one sulfur atom in their molecules.

[0068] Among these sulfur containing aromatic amines there may be citedthe amines of formula:

[0069] and mixtures thereof;

[0070] in which R represents a hydrogen atom or an alkyl group,preferably a C₁ to C₆ alkyl group and more preferably a methyl group,and

[0071] R′ is an alkyl group, preferably a C₁ to C₆ alkyl group, and morepreferably a methyl group.

[0072] It is possible to replace part of the polyurea segments of thefinal material by adding one or more of the following monomers to thearomatic diamine in the second step of polymerization.

[0073] Thus, a polyurea segment can be replaced by a hard urethaneand/or a thiourethane segment by adding a cycloaliphatic or aromaticdiisocyanate such as xylylène diisocyanate and/or a diol or a dithiolsuch as:

HS—CH₂CH₂—S—CH₂CH₂—SH

[0074] A polyurea segment can also be partly replaced by highlycrosslinked areas by adding to the amine during the second step ofpolymerization tri and tetra alcohols and/or thiols such as:

[0075] or polythiols such as those of formula:

[0076] and mixtures thereof,

[0077] or polyols such as those of formula:

HO—CH₂—CHOH—CH₂OH

HS—CH₂—CHOH—CH₂OH

HS—CH₂CHOH—CHOH—CH₂—SH

[0078] This second reaction step is effected by simply mixing prepolymer(III) with the diamine (IV) and the optional additional monomers, ifany, and by heating at a temperature above 100° C., generally rangingfrom 100° C. to 130° C. up to the obtention of the final curedpolythiourethane/urea material.

[0079] Conventional additives such as inhibitors, dyes, UV absorbers,perfumes, deodorants, antioxydants, antiyellowing agents and releaseagents may be added to the material of the present invention in theusually used quantities.

[0080] These additives may be added either in the first step or in thesecond step of preparation of the final material, but are preferablyadded during the second step.

[0081] The following examples illustrate the present invention. In theexamples, unless otherwise stated, all parts and percentages are byweight.

[0082] I. Examples of Synthesis of Polysulfides of Formula (I_(c))

[0083] I.1 Preparation of polysulfides PS1 to PS7.

[0084] The polymerization reaction between AS and DMES was carried outin the presence of a photoinitiator, under UV. The equipment used togenerate the UV light was an EFOS Ultracure 100 SS PLUS equipped with anoptic fiber (lamp #320-60651).

[0085] The UV light was shined above the surface of the monomer mixture.The light intensities reported were measured using a UV-MO2 irradiancemeter equipped with a UV-35 sensor (320-390 nm sensing wavelength).Several experimental conditions were studied in order to maximize therefractive index of the reaction product as well as the allylconversion. The experimental conditions and the results are reported inTable I.

[0086] Two photoinitiators were tried: 1-hydroxycyclohexyl phenyl ketone(Irgacure® 184) and 2-hydroxy-2-methyl-1-phenyl-propan-1-one (Darocur®1173). As shown in Table 1 (runs PS1 and PS2), a significant increase ofthe refractive index of the mixture was noticed in both cases. Therefractive index of the polymer made was about the same between the twoinitiators. Darocur® 1173 is a liquid that is easier to handle and todisperse in the monomer mixture than Irgacure® 184 (which is a powder).Thefore, Darocur® 1173 is preferably used in the experiments. TABLE I UVexposure n_(D) (25° C.) Allyl DMES AS Photoinitiator PhotoinitiatorMolar ratio Time UV Intensity after UV conversion Run (g) (g) (g) (%)Allyl/SH (s) (mW) exposure (%) PS1 a) 10.0102 5.4698 0.3358 2.123 0.738 5 × 60 51 1.5800 PS2 b) 9.9916 5.4661 0.1635 1.047 0.739  5 × 60 511.5797 PS3 b) 10.0305 5.4952 0.3340 2.106 0.740  5 × 60 51 1.5813 PS4 b)9.9961 5.4676 0.8129 4.994 0.739 10 × 60 40 1.5864 c) 58 PS5 b) 9.99145.4658 0.8105 4.982 0.739 10 × 60 90 1.5869 68 PS6 b) 10.0135 5.4802 5 ×0.1622 5.075 0.739 5 × 3 + 1) × 60 50 1.5974 d) 93 PS7 b) 9.9991 5.46740.8202 5.036 0.739 960 50 1.5901 d) 76

[0087] Allyl conversion is measured by FTIR according to the followingformula:${{Allyl}\quad {conversion}\quad (\%)} = {100 \times \left( {1 - \frac{{Intensity}\quad {of}\quad {the}\quad 1636\quad {cm}^{- 1}{{signal}/{intensity}}\quad {of}\quad {the}\quad 1672\quad {cm}^{- 1}\quad {signal}\quad {after}\quad {reaction}}{{Intensity}\quad {of}\quad {the}\quad 1636\quad {cm}^{- 1}{{signal}\quad/{intensity}}\quad {of}\quad {the}\quad 1672\quad {cm}^{- 1}\quad {signal}\quad {before}\quad {reaction}}} \right)}$

[0088] The 1636 cm⁻¹ signal corresponds to the allyl group. The 1672cm⁻¹ signal corresponds to the phenyl groups of the photoinitiator andwas used as an internal reference.

[0089] As shown in Table I (PS2 and PS3), the refractive index of thepolymer made shows a slight increase when the photoinitiatorconcentration is varied between 1.0% and 2.1%.

[0090] The increase of the UV intensity from 40 mW to 90 mW results inslight increase of the refractive index of the polymer and a higherconversion of the allyl groups (Table I, PS4 and PS5). On the otherhand, the increase of the UV exposure time from 600 s to 960 s resultedin a significant increase of both the refractive index and the allylgroups conversion (Table I, PS6 and PS7).

[0091] As reported in Table I, PS6 and PS7 where polymerized with thesame amount of photoinitiator added to the monomer mixture, either infive shots (PS6) or in one shot (PS7). The results show that theincrease of the refractive index of the polymer and the conversion ofthe allyl groups were much higher when the photoinitiator was added infive shots. Under these conditions, a refractive index (n_(D) ²⁵) of1.5974 and an allyl conversion of 93% were reached.

[0092] I.2 Preparation of Polysulfides PS8 to PS10

[0093] The polymerization reaction between AS and DMES was carried outas previously mentioned using the quantities and conditions indicated inTable II. In particular a fusion lamp system equipped with a D Bulb wasused for polymerizing PS10. TABLE II n_(D) (25° C.) Allyl DMES ASPhotoinitiator Photoinitiator after UV conversion {overscore (M)}n RunUV equipment (g) (g) (g) (%) Allyl/SH exposure (%) (g · mol − 1) PS8 b)Optic fiber 90.10 49.32 5 × 1.4564 5.065 0.740 1.5790 54 PS9 b) Opticfiber 90.11 49.32 5 × 1.471  5.101 0.740 1.5816 57 PS10 c) Fusion system90.09 49.39 5 × 1.4470 4.931 0.741 1.6090 98 1080

[0094] I.3 Preparation of polysulfides PS11 to PS13

[0095] The polymerization reaction between AS and DMES was usuallycarried out in bulk or in the presence of tetrahydrofuran (THF) as asolvent, with the conditions indicated in Table III.

[0096] The allyl conversion in the final product was similar to the oneobtained in the absence of THF. TABLE III n_(D) ²⁵ Allyl DMES AS THFPhotoinitiator Photoinitiator UV exposure after UV Conversion Run (g)(g) (g) (g) (%) Ally/SH Time (min) exposure (%) PS11 10.0262 5.4818 0 5× 0.1613 4.944 0.739 5 × 3.5 1.6084 97 PS12 10.0262 5.4818 0 5 × 0.16134.944 0.739 5 × 3.5 + 3 × 3.5 1.6112 96 PS13 10.0193 5.4799 13.0431 5 ×0.1649 2.808 0.739 5 × (3 × 1.2) 96

[0097] I.4 Preparation of polysulfides PS14 to PS21

[0098] All the experiments carried out so far used an Allyl/SH molarratio of about 0.739. In order to study the effect of this molar ratioon the properties of the polysulfides made, a series of experiments havebeen conducted where the Allyl/SH molar ratio was varied from 0.500 to1.354. The experimental conditions as well as the results of thesesyntheses were reported in Table IV.

[0099] As shown, the refractive indexes, the allyl conversion andprecipitation yields of the polysulfides were all similar to each other.

[0100] The refractive index n_(D)²⁵

[0101] was around 1.611 for most the precipitated polymers, which ishigher than of the LP-33 polysulfide, a polysulfide having —S—S—linkages from Morton International ( (n_(D)²⁵ = 1.559).

[0102] ).

[0103] Structures of the polysulfides were confirmed by H NMR and 13CNMR spectrum. TABLE III n_(D) ²⁵ n_(D) ²⁵ Allyl n_(D) ²⁵ of {overscore(M)}_(n) DMES AS Photoinitiator Photoinitiator before UV after UVconversion Yield precipitate (g · Run (g) (g) (g) (%) Allyl/SH exposureexposure (%) (%) d polymer mol⁻¹ ) PS14 10.9512 4.0532 5 × 0.1602 5.0680.500 1.5642 1.6072 95 72.1 1.6125 650 PS15 9.7001 5.3094 5 × 0.15544.921 0.740 1.5581 1.6067 90 76.5 1.6122 860 PS16 8.9964 5.9973 5 ×0.1579 5.002 0.901 1.5488 1.6064 87 80.3 1.6092 1080 PS17 8.6277 6.36545 × 0.1578 5.001 0.997 1.5480 1.6044 80 75.1 1.6106 1100 PS18 8.62476.3781 5 × 0.1597 5.054 0.999 1.5432 1.6032 81 64.8 1.6112 1070 PS198.5813 6.4342 5 × 0.1562 4.944 1.013 1.5464 1.6065 86 74.4 1.6124 1050PS20 8.2525 6.7829 5 × 0.1609 5.080 1.111 1.5402 1.6052 84 73.0 1.61051120 PS21 7.4855 7.5026 5 × 0.1583 5.015 1.354 1.5348 1.6058 85 71.01.6116 1320

[0104] The SH content of the polysulfides was measured by titrationusing iodine. As expected, the SH content decreased with the increase ofthe Allyl/SH molar ratio. When Allyl/SH=0.5, the end groups consistalmost exclusively of SH, and the value of {overscore (M)}_(n)calculated from the SH content assuming 100% SH end groups is very closeto the one measured by GPC.

[0105] I.5 Preparation of Polysulfide PS22

[0106] In a 100 ml three necked flask equipped with a magnetic stirrer,a heating mantle, an inlet for an inert gas on one port and a condenseron another port, we introduce 30.2016 g DMES, 16.4094 g Ally sulfide(Allyl/SH=0.734) and 2.6250 g 2,2′-Azobisisobutyronitrile (AIBN)previously dried, 2,2′-Azobisisobutyronitril (AIBN) received fromMonomer-Polymer and Dajac Laboratories, Inc.

[0107] The mixture is heated to 65° C. Stirring was continued until theFTIR signal at 1636 cm⁻¹ corresponding to the allyl groups disappeared(43 hours). This shows that AIBN is an effective initiator. Therefractive index n_(D)²⁵

[0108] of the mixture at this time was 1.6092. This product is dissolvedin about 46 g of THF, and the solution is precipitated drop-wise in twoliter of methanol.

[0109] After 24 hours, the supernant methanol solution is removed, andthe white precipitate is dried under vacuum at room temperature.

[0110] The precipitation yield was about 80%. The refractive indexn_(D)²⁵

[0111] of the precipitated polysulfide was 1.6140. Its molecular weightby GPC was {overscore (M)}_(n)=900 g×mol−1 ({overscore(M)}_(W)/{overscore (M)}_(n)=1.685). Its SH content measured bytitration was 2.157 mmol SH/g ({overscore (M)}_(n)=930 g×mol⁻¹ based on(α, ω) SH chains).

[0112] Although the polymerization reaction between DMES and AS issuccessful when using a thermal radical initiator, the UV polymerizationis a preferred polymerization method since the reaction times are muchshorter (27 minutes in UV polymerization versus 43 hours in thermalpolymerization).

[0113] II. Example of Synthesis of (α, ω)-diiso(thio)cyanate Prepolymer(III)

[0114] The synthesis of these prepolymers was carried out under ablanket of dry nitrogen, at different temperatures, in the presence orabsence of dimethyltindichloride catalyst. Several NCO/SH molar ratioswere used. The reaction was followed by infra-red spectrometry for theNCO conversion (NCO signal at 2262 cm⁻¹), Raman spectroscopy for the SHconversion (SH signal at 2520 cm⁻¹) and by measuring the refractiveindex. After the reaction was stopped (by removing the heat source), theNCO content of the prepolymers was measured by titration.

[0115] Starting components, quantities and reaction conditions are givenin Table V below. TABLE V At the end of At the end of NCO- ReactionReaction reaction reaction terminated Polysulfide Desmodur ® WTemperature Time % NCO res. % SH res. n_(D) ²⁵ prepolymer Polysulfide(g) (g) (° C.) (hrs) (FTIR) (RAMAN) after synthesis 1 PS10 52.10 39.72110 144 73.8 3.5 1.5760 A LP-33 146.71 116.09 110 41 75.7 6.5 1.5411

[0116] Desmodur® W was Provided by BAYER:

[0117] Physical state: slurry at RT (melting point: 40-50° C.)

[0118] Purity (NCO titration): 97.3% (NCO content measured was 31.2%,31.8% according to Bayer)

[0119] Refractive index n_(D) at 45° C.: 1.4950

[0120] Specific gravity at 25° C.: 1.07

[0121] III. Obtention of the Polythiourethane/Urea Material

[0122] NCO terminated prepolymer 1 obtained in step II above was reactedwith Ethacure®-300 (which is a 80:20 mixture of the 2,4- and 2,6-isomersof dimethylthiotoluenediamine), and filled into −2.000 dioptries glassmolds to make a lens. The experimental conditions of the casting and theproperties of the lense are reported in Tables VI and VII. They showthat the use of the polysulfide PS10 allows to reach a refractive indexof 1.615, a good impact resistance.

[0123] Ethacure®-300 monomer was provided by Albermarle Corporation. Itis an approximate 80:20 mixture of the 2,4- and 2,6-isomers ofdimethylthiotoluenediamine, and has the following characteristics:

[0124] Physical state: liquid

[0125] Color: clear amber, darkens with time, upon exposure to air

[0126] Refractive index n_(D) at 25° C.: 1.6642

[0127] Specific gravity at 20° C.: 1.208

[0128] Viscosity at 20° C.: 690 cSt

TABLE VI NCO Ethacure ® Degas Degas Prepolymer 1. 300 Molar ratio Time.Temp. Mix. Time Mix. Temp (g) (g) NH2/NCO. (mn) (° C.) (mn) (° C.) CureCycle Example 1 30.1799 5.9137 0.940 30 110 3 110 8 hrs/130° C.

[0129] TABLE VII Formulations Dynatup Impact/Center NCO (Prepolymer +Index thickness Soft. Modulus (E′) Modulus (E′) Run Prepolymer Amine)NH2/NCO (n_(D) ²⁵) Density of the −2.00 lens Temps* at 25° C.** at 100°C. Example 1 1 83.62% + 16.38% 0.940 1.615 1.21 133 in-lb/1.16 mm >80°C. 8.1 × 10⁸ Pa 1.7 × 10⁸ Pa (1.532 kg · m) Example A A 79.2% + 20.1%0.931 1.592 1.25 111 in-lb/1.30 mm >80° C. — (comparative) (1.279 kg ·m) Example B A 79.86% + 20.14% 0.932 1.592 1.25 160 in-lb/2.10 mm >80°C.   8 × 10⁸ Pa   2 × 10⁸ Pa (comparative) (1.843 kg · m)

[0130] The results of Table VII show that the material of the inventionexhibits both a higher refractive index and high impact resistance.

[0131] Impact energy (Dynatup) was measured using an impact test machinedesigned by General Research Corp. (Model 8210 Drop Weight Impact TestMachine). This machine has the capability to test materials over a widerange of velocities and energies. The velocities can reach up to 4.5m/sec with a maximum standard drop eight of 36 inches. The cross-headweight can vary from approximately 4.1 to 27 kg.

[0132] E′ modulus is measured by dynamic mechanical analysis (DMA) usinga Perkin Elmer DMA 7e equipment (3-point bending, heat from 5° C. to180° C. at 2° C./min and a frequency of 1 Hz).

What is claimed is:
 1. A transparent, non-elastomeric, high index,impact resistant polythiourethane/urea material comprising the reactionproduct of: a) at least one (α, ω)-diiso(thio)cyanate prepolymer havinga number average molecular weight ranging from 100 to 3000 gmol⁻¹, saidprepolymer being free from disulfide (—S—S—) linkage, and b) at leastone aromatic primary diamine, in an equivalent molar ratio aminefunction/iso(thio)cyanate function (NH₂/NCX, X=O, S) ranging from 0.5 to2, preferably 0.90 to 1.10, said aromatic primary diamine being freefrom disulfide (—S—S—) linkage, and wherein, at least one of theprepolymer or the diamine contains one or more S atoms in its chain. 2.The material of claim 1, wherein the equivalent ratio NH₂/NCX rangesfrom 0.93 to 0.95.
 3. The material of claim 1, wherein the (α,ω)-diiso(thio)cyanate cycloaliphatic or aromatic prepolymer is thereaction product of at least one (α, ω) diol or dithiol prepolymer andat least one cycloaliphatic or aromatic diiso(thio)cyanate.
 4. Thematerial of claim 3, wherein the (α, ω) diol or dithiol prepolymercontains at least one S atom in its chain.
 5. The material of claim 3,wherein the (α, ω) diol or dithiol prepolymer is a polysulfide or amixture of polysulfides.
 6. The material of claim 5, wherein thepolysulfide or mixture of polysulfides is selected from the groupconsisting of: Prepolymers of formula:

in which x and y are such that the number average molecular weight ofthe prepolymer ranges from 100 to 3000 gmol⁻¹;
 7. The material of claim5, wherein the polysulfide is an hyperbranched polysulfide.
 8. Thematerial of claim 1, wherein the aromatic diamine contains at least oneS atom in its molecule.
 9. The material of claim 8, wherein the diamineis selected from

in which R is H or an alkyl group and R′ is an alkyl group, and mixturesthereof.
 10. The material of claim 1, wherein in step (2) the (α,ω)-diiso(thio)cyanate prepolymer is also reacted with a di-, tri- ortetra alcohol, a di-, tri or tetrathiol or a mixture thereof.
 11. Thematerial of claim 10, wherein the di-, tri- and tetra alcohols andthiols are selected from the groups consisting of:

and mixtures thereof.
 12. The material of claim 1 having a refractiveindex, n_(D)²⁵,

higher than 1.53.
 13. The material of claim 1 having a refractive index,n_(D)²⁵,

of at least 1.55.
 14. The material of claim 1 having a refractive index,n_(D)²⁵,

of at least 1.57.
 15. An optical article made from a material accordingto claim
 1. 16. The optical article of claim 15, wherein said article isselected from the group consisting of sun lenses, ophthalmic lenses andprotective lenses.
 17. A polysulfide of formula:

wherein n is such that the number average molecular weight of thepolysulfide ranges from 500 to 1500 gmol^(−1.)
 18. The polysulfide offormula 17 having a number average molecular weight ranging from 650 to1350 gmol⁻¹.
 19. A process for making a polysulfide of formula:

wherein n is such that the number average molecular weight of thepolysulfide ranges from 500 to 1500 gmol⁻¹, which comprises irradiatingwith a UV light a mixture of 2-mercaptoethylsulfide and allylsulfide inthe presence of a photoinitiator.
 20. The process of claim 19, whereinthe photoinitiator is added in several shots during the irradiationprocess.
 21. A process for making a polysulfide of formula:

wherein n is such that the number average molecular weight of thepolysulfide ranges from 500 to 1500 gmol⁻¹, which comprises thermallypolymerizing a mixture of 2-mercaptoethylsulfide and allylsulfide in thepresence of a thermal initiator.